From the experimental studies on the development and establishment of the evaluation method of the separation characteristics for nano-meter particles in gas-phase, the following results were obtained.(1) Two types of generation method of nanometer-size particles were developed experimentally : One is based on the thermal decomposition of metal alkoxide vapor such as titanium, silicon and aluminium, and the other on the radiolysis of SO_2/H_2O/N_2 mixture. The number and size distribution of generated particles were measured by the differential mobility analyzer (DNA) and the Faraday cup electrometer (FCE). In these methods, the nanometer size particles around 2nm in average diameter can be generated stably.(2) In order to classify the nanometer-sized particles by the electrical mobility analyzer, a new type of electrical mobility analyzer (Cluster Type Differential Mobility Analyzer) was developed, and the ion and molecular clusters can be classified successfully.(3) In order to detect the concentration of charged ions and clusters, a new type of Faraday cup electrometer was developed and the charged quantity of cluster was detected down to 10^<-15>A.(4) With the generated cluster flowing through the screen or pipe, the removal characteristics were evaluated experimentally. For the clusters smaller than about 2 nm, the sticking probability of clusters onto a wall became smaller than unity. This rebounding characteristics depended on particle and wall materials.(5) Combining the generation method and detection method enabled us to evaluate the removal characteristics of nanomter particles in gas-phase.